1. Field of the Invention
The present disclosure relates to a fixing device and an image forming apparatus.
2. Description of the Related Art
The image forming apparatus includes a fixing device for heating a recording sheet having a toner image transferred thereon and fixing the toner image to the recording sheet.
The above device causes a fixing roller to generate heat by switching on and off a switching element to change the magnitude and direction of a magnetic flux generated by an induction coil.
Self-heat generation occurs when the switching element is turned on and off. The switching element is destroyed if the temperature thereof reaches a destruction temperature (absolute maximum rating), which is a temperature at which the switching element is destroyed, due to such self-heat generation.
Accordingly, to prevent the temperature of the switching element from reaching the destruction temperature, a temperature sensor for detecting the temperature of the switching element is arranged and this image forming apparatus stops the on/off switching of the switching element when the temperature of the switching element detected by the temperature sensor reaches a predetermined temperature. This prevents the temperature of the switching element from reaching the destruction temperature to destroy the switching element.
The temperature of the switching element detected by the temperature sensor is thermally conducted from the switching element to the temperature sensor. Thus, there is a difference between the temperature detected by the temperature sensor and the temperature of the switching element. Further, such a temperature difference also changes depending on an operating condition of the image forming apparatus.
Thus, if the on/off switching of the switching element is stopped when the temperature detected by the temperature sensor reaches the predetermined temperature as described above, the stop of the on/off switching of the switching element may be late for a temperature change of the switching element. Therefore, it has been difficult to reliably protect the switching element from destruction caused by heating.